This meeting on lnterleukin 12 (IL-12, a cytokine central to the induction of a cellular immune response, and important in viral, microbial, and tumor immunology) is intended to bring together investigators working within the various disciplines together. By means of this conference we will expect that new insights will arise because of the cross fertilization that will result form individuals working within the broad areas of infectious disease including those studying lL- 12's role in AIDS, those interested in its apparent role in cancer (based on murine studies) and those interested in its immunoregulation. Interleukin-12 is a heterodimeric cytokine originally defined by its ability to induce the maturation of cytolytic lymphocytes and by its capacity to effectively synergize with IL-2 in the induction of cytolytic activity. IL-12 activates NK cells, facilitates the generation of specific cytolytic T lymphocytes (CTL), maintains tumor infiltrating lymphocytes (TIL) in culture, and induces the secretion of high levels of IFN-gamma (required early in the immune response) from both T cells and NK cells in vitro. While IL-2 may promote similar functions, IL-12 is effective at concentrations 10-1000fold less than IL-2. Since IL-12 is secreted exclusively by "professional" antigen presenting cells and IL-12 receptors are expressed selectively on activated T lymphocytes and NK cells, it appears that IL-12 is well suited to drive the expansion and maturation of the two most prevalent effector cells (T cells and NK cells). These findings indicate that IL-12 may be an ideal candidate for use in the immunotherapy of solid tumors and the development of effective tumor and microbial vaccines. This conference will focus on the emerging understanding of the biology of IL-12 including its production, receptor interactions, signal transduction, interactions with other cytokines, its use as a therapy for AIDS and cancers and its role in promoting an effective cellular response to microbial pathogens. We have been particularly sensitive to the needs of the more junior and promising investigators, including them, where appropriate on the program, and by having optimum time for interaction and presentation at poster sessions. Given the current great interest in IL-12, we believe that this meeting will likely serve as a benchmark for those working in the field at multiple levels.